This invention relates to the testing of digital-to-analog converters.
Digital-to-analog conversion refers to a process in which signals having a finite number of defined levels or states are converted into signals having a theoretically infinite number of levels or states. A circuit that performs that function is a digital-to-analog converter (DAC). A current output DAC produces a current output having a magnitude that typically is proportional to an n-bit digital word provided to the device, where n is a positive integer. The DAC can, therefore, be viewed as a digitally controlled current source in which the level of the current produced by the source is proportional to the digital word fed to the device.
The current output signal from the DAC typically is converted into a proportional voltage. In such a situation, the DAC does not operate as an ideal current source because of the DAC""s internal impedance. As a result of the current through the internal impedance, the output current changes slightly from that defined by the digital word fed to the DAC. The change or variation in the desired output current as a function of output voltage is indicative of the compliance voltage range of the DAC. The compliance voltage range refers to the maximum range of output terminal voltage for which the DAC will provide a specified current output characteristic.
Frequently it is desirable to determine the compliance voltage range of a DAC. For example, the compliance voltage range can be measured and provided to users of the DAC so that they can determine whether the device is suitable for their particular applications.
When one or more DACs are incorporated into an electronic device or system, the DACs may be tested during the manufacture of the device or system. Preferably, the testing should be performed sufficiently quickly so that the testing does not significantly slow down the production process. At the same time, it is important that the testing provide a relatively high degree of accuracy over a wide range of input and output values.
In general, a technique for testing digital-to-analog converters includes providing a set of digital input signals to the digital-to-analog converters and comparing a resulting combined output signal from the digital-to-analog converters to a comparison value. A determination is made as to whether the resulting combined output signal is within a predetermined tolerance defined by the comparison value. An apparatus for testing digital-to-analog converters also is disclosed.
Various features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims.